SLIMONIA ACUMINATA. 



113 



into the external angle of the coxal joint, where it is nine lines broad and expanding late- 

 rally at its distal end to 1^ inches, so as to embrace in its cup-shaped and rounded lower 

 border the conjoined ischium and meros. 



The Ischium and Meros resemble an oblong square divided diagonally, the ischium 

 having its upper and proximal border 11 lines broad, and its lower end cut off by the 

 distal termination of the meros, which is one inch broad, 

 whilst the proximal end of the meros is in like manner 

 cut off by its union with the ischium. 



The ischium along its inner longitudinal free border 

 measures one inch ; the meros along its outer rounded 

 free border measures 1^ inches ; the conjoined border 

 measures 16 lines in length. 



The carpus resembles the basos in form ; it is ten 

 lines broad at the upper and five lines long and slightly 

 expanded at the lower border, which is curved so as to 

 afford a better articulation to the propodos. 



The propodos is two inches long and ten lines broad, 

 and its sides are nearly parallel ; it is excavated at the lower 

 extremity, so as to admit the insertion of the dactylus. 



Between these two on the inner side is a small trian- 

 gular plate intercalated, four lines in length and three in 

 breadth ; a similar plate is known to exist in Eurypterus 

 and other forms. 



The dactylus is 1^ inches long and half an inch 

 broad ; near its termination a minute plate {unguis) is 

 inserted ; a similar terminal plate is noticed by Professor 

 Hall in Eurypterus. The border of these joints is some- 

 times seen to be slightly crenated. 



Post-oral Plate or Metastoma (PI. XVII, fig. 1, m; 

 PI. XVIII, fig. 1, m). — This plate is seen in situ in 

 Pis. XVII and XVIII ; the largest lip-plate of Slimonia 

 known is that figured in the subjoined woodcut (fig. 33) 

 of the natural size. It measures 5-g- inches in length 

 and If inches in greatest breadth, the lower part bein g 

 only ten lines broad. Its greater length as compared to 

 its breadth distinguishes it at once from the metastoma 

 of Pterogotus, with the remains of which Slimonia is 

 commonly found associated. 



The upper end {a) is deeply bilobed, the lobes elliptical and the notch very narrow ; its 

 greatest breadth (If in.) is in the centre of the upper two thirds; the lower third is very 



Fig. 33. — Largest lip-plate of Slimonia 

 acuminata known, from Upper 

 Ludlow Rock, Lesmahagow. Ori- 

 ginal preserved in the British 

 Museum. 



